KB Article: http://support.microsoft.com/kb/2638243

INTRODUCTION

 An NTP client computer that is running Windows Vista, Windows Server 2008, Windows 7, or Windows Server 2008 R2, may not correct the time if the following conditions are true:

  • The NTP client syncs its time with the manually specified NTP server.
  • The NTP client uses SpecialPollInterval as a polling interval.
  • The time offset between the NTP client and the NTP server is greater than the LargePhaseOffset as configured in the NTP client.

In this situation, the NTP client cannot correct its time even after waiting for SpikeWatchPeriod to pass.